Re: [gtk-list] Re: Signals and callbacks

[Karl Mitchell <k l mitchell lancaster ac uk>]

Rodrigo Moya wrote:

> Hi!
>
> >Secondly, signals and callbacks. I'm trying to implement a simple zoom
> routine
> >for each image, activated whenever the event box holding the image is
> clicked,
> >at present using:
> >
> >    gtk_signal_connect (GTK_OBJECT (event_box_right), "button_press_event",
> >        GTK_SIGNAL_FUNC (magnify_image), NULL);
> >
> >However, the magnify_image function needs quite a lot of information passed
> to
> >it:
> >
> >    struct _imageData{
> >        GdkImlibImage *image;
> >        GtkWidget *pixmapwidget;
> >        gint magnification_factor;
> >    }
> >
> >, and for the life of me I can't work out how to do it. I think it's
> something
> >to do with my lack of understanding of gpointers. Could anyone help me work
> >this one out?
> >
> If what you mean is how to pass this data to the callback, you should
> replace the above function line with:
>
>     gtk_signal_connect (GTK_OBJECT (event_box_right), "button_press_event",
>         GTK_SIGNAL_FUNC (magnify_image),  (gpointer) &_imageData);
>
> replacing _imageData with the name of the variable you want to pass.
> gpointer is just a void *.
>
> I hope this was what you were asking.

That's about it. Thankyou! So how do you access the structure data in the
magnify_image function? I always seem to get confused when passing pointers
around the place.

-Karl

--
 =-=-=-=-=-=-=-=-=-=-=-=-=-=-Karl Mitchell=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
| Planetary Science Research Group |     Secretary, ISPRS WG IV/5      |
|   Environmental Sciences Dept.   |    "Extraterrestrial Mapping"     |
|  I.E.N.S., Lancaster University  | http://www.ge.ucl.ac.uk/isprs-etm |
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